How to Use a Continuous Glucose Monitor (CGM) for Better Blood Sugar Management

18 Sep 2025 By Rachael C. Passmore, D.O.

How to Use a Continuous Glucose Monitor (CGM) for Better Blood Sugar Management

Managing blood sugar levels effectively is crucial for people with diabetes, but it can be a challenging task. Traditional methods, such as finger-prick blood glucose testing, provide a snapshot in time. However, continuous glucose monitors (CGMs) offer a dynamic view of glucose levels, empowering users to make more informed decisions about their health. This article will guide you on how to use a CGM for improved blood sugar management, covering everything from the basics of CGMs to advanced strategies.

What is a Continuous Glucose Monitor (CGM)?

A Continuous Glucose Monitor (CGM) is a device that tracks glucose levels in real-time throughout the day and night. Unlike traditional blood glucose meters (BGMs) that require a finger prick for each reading, a CGM uses a small sensor inserted under the skin to measure glucose levels in interstitial fluid (the fluid surrounding cells).

Here’s a quick comparison:

| Feature | Blood Glucose Meter (BGM) | Continuous Glucose Monitor (CGM) | |-----------------------|---------------------------------|---------------------------------------| | Measurement | Snapshot in time | Continuous, real-time tracking | | Method | Finger prick | Sensor inserted under the skin | | Data Provided | Single data point | Trend data, patterns, alerts | | Convenience | Less convenient (multiple daily)| More convenient (continuous monitoring)| | Cost | Lower upfront cost | Higher upfront cost |

Why CGMs Are a Game-Changer:

Real-Time Data: CGMs provide immediate feedback on how food, exercise, stress, and medication affect blood sugar.
Trend Information: They show whether glucose levels are rising, falling, or stable, helping to predict and prevent highs and lows.
Customizable Alerts: CGMs can be set to alert users when glucose levels go too high or too low, even during sleep.
Reduced Finger Pricks: While some CGMs may require occasional finger-prick calibration, they significantly reduce the need for frequent blood glucose testing.
Improved A1c: Studies have shown that consistent CGM use can lead to better glycemic control, resulting in lower A1c levels.

Types of Continuous Glucose Monitors (CGMs)

Several CGM systems are available, each with unique features and benefits. The most popular include:

Dexcom G6 and G7: Known for their accuracy and user-friendly interface, Dexcom systems transmit data to a receiver or smartphone app every five minutes. They offer customizable alerts and integration with insulin pumps.
Abbott FreeStyle Libre: This system uses a sensor that lasts up to 14 days and provides glucose readings when scanned with a reader or smartphone. It doesn't require routine finger-prick calibration.
Medtronic Guardian Connect: Integrated with Medtronic insulin pumps, this CGM provides predictive alerts and real-time glucose data to help manage insulin delivery.
Eversense CGM: A long-term implantable CGM that lasts up to six months. It provides continuous glucose readings and alerts through a smart transmitter.

The following table summarizes the key aspects of these CGM systems:

| CGM System | Sensor Duration | Calibration Required | Data Transmission | Key Features | |--------------------------|-----------------|----------------------|-------------------|-----------------------------------------------------------------------------------------------------------| | Dexcom G6/G7 | 10 days | No | Bluetooth to App | Real-time readings, customizable alerts, integration with insulin pumps | | Abbott FreeStyle Libre | 14 days | No | Scanning | Factory-calibrated, no finger-prick calibration, trend arrows | | Medtronic Guardian Connect | 7 days | Yes | Bluetooth to App | Predictive alerts, integration with Medtronic insulin pumps, continuous monitoring | | Eversense CGM | Up to 6 months | Yes | Bluetooth to App | Long-term implantable sensor, alerts via smart transmitter, continuous glucose readings | A Complete Normal Blood Sugar Chart For Adults With And Without Diabetes

Choosing the right CGM system depends on individual needs, preferences, and budget. Consult with your healthcare provider to determine the best option for you.

Step-by-Step Guide to Using a CGM

Using a CGM effectively involves understanding its components, proper insertion techniques, data interpretation, and troubleshooting. Here's a detailed guide to help you get started:

1. Preparing to Use a CGM

Before you begin, ensure you have everything you need:

CGM System Kit: Includes the sensor, transmitter (if applicable), and applicator.
Receiver or Smartphone: For viewing glucose data.
Alcohol Swabs: For cleaning the insertion site.
Instruction Manual: Read it thoroughly.
Sharps Container: For disposing of used sensors.

Checklist Before Insertion:

Review the Instructions: Each CGM system has specific instructions. Take the time to read and understand them.
Choose the Insertion Site: Select an appropriate site as recommended by the manufacturer. Common sites include the abdomen or upper arm.
Clean the Site: Use an alcohol swab to clean the insertion site thoroughly. Allow it to dry completely.

2. Inserting the CGM Sensor

Each CGM system has a unique insertion method, but the general steps are as follows:

Prepare the Applicator: Follow the manufacturer's instructions to load the sensor into the applicator.
Apply the Sensor: Press the applicator firmly against the cleaned skin and push the button to insert the sensor.
Attach the Transmitter (if applicable): Some systems require attaching a transmitter to the sensor to send data to the receiver or smartphone.
Secure the Sensor: Use adhesive patches or tape to secure the sensor in place.

Tips for Painless Insertion:

Rotate Insertion Sites: To avoid skin irritation, rotate the insertion site each time you change the sensor.
Avoid Areas with Scars or Stretch Marks: These areas may not provide accurate readings.
Hydrate: Well-hydrated skin can make insertion easier and more comfortable.
Apply Pressure: Use firm, even pressure when applying the sensor.

3. Calibrating the CGM (if required)

Some CGMs require calibration with finger-prick blood glucose readings. Follow the manufacturer's instructions for calibration. Generally, this involves:

Performing a Finger-Prick Test: Use a blood glucose meter to measure your blood sugar.
Entering the Value into the CGM: Input the blood glucose value into the CGM receiver or smartphone app.
Follow the Calibration Schedule: Calibrate as often as recommended by the manufacturer.

Calibration Best Practices:

Calibrate When Stable: Avoid calibrating when your glucose levels are rapidly rising or falling.
Use a Reliable Meter: Ensure your blood glucose meter is accurate and well-maintained.
Follow Instructions: Adhere to the manufacturer's calibration schedule and guidelines.

4. Monitoring Glucose Data

Once the sensor is inserted and calibrated, you can start monitoring your glucose data. The CGM will display real-time glucose readings, trend arrows, and historical data.

Understanding the Data:

Glucose Readings: The current glucose level in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L).
Trend Arrows: Indicate the direction and speed of glucose changes (rising, falling, or stable).
Glucose Graphs: Show glucose levels over time, helping to identify patterns and trends.

Here is an example of how to interpret CGM data using the FreeStyle LibreLink app:

Scan Your Sensor: Pass your smartphone or FreeStyle Libre reader over the sensor to receive data.
View Your Glucose Reading: The top left corner displays your current glucose level.
Check the Trend Arrow: Directly below your current glucose reading is the trend arrow that tells you the direction your glucose is heading.

5. Setting Alerts and Alarms

One of the key benefits of CGMs is their ability to provide alerts and alarms when glucose levels go outside the target range. Customize these settings to meet your individual needs.

Types of Alerts:

High Glucose Alert: Notifies you when your glucose level exceeds a pre-set threshold.
Low Glucose Alert: Alerts you when your glucose level drops below a pre-set threshold.
Urgent Low Glucose Alert: Provides a warning when your glucose is dangerously low.
Rate of Change Alert: Alerts you when your glucose level is rising or falling rapidly.

Customizing Alert Settings:

Set Target Ranges: Work with your healthcare provider to determine appropriate target glucose ranges.
Adjust Alert Thresholds: Configure the alerts to trigger based on your target ranges.
Choose Alert Sounds: Select distinct alert sounds to differentiate between different types of alerts.

Interpreting CGM Data and Making Informed Decisions

CGMs provide a wealth of data that can be used to optimize blood sugar management. Learning how to interpret this data and make informed decisions is essential.

1. Identifying Patterns and Trends

Use the CGM data to identify patterns and trends in your glucose levels. Look for:

Time of Day Effects: How glucose levels change at different times of the day.
Meal-Related Changes: How specific foods and meals affect glucose levels.
Exercise Impact: How physical activity influences glucose levels.
Medication Effects: How medications affect glucose levels.

Example Scenario:

Imagine a patient notices that their glucose levels consistently spike after eating pizza. By identifying this pattern, they can adjust their insulin dosage, choose a different meal, or reduce their portion size to avoid the spike. Normal Blood Sugar Levels Your Complete Chart By Age And Time Of Day

2. Adjusting Insulin Dosages

If you use insulin, CGM data can help you fine-tune your dosages. Work with your healthcare provider to adjust your basal and bolus insulin based on your CGM readings.

Basal Insulin Adjustments:

Review Overnight Glucose Data: If your glucose levels are consistently high or low overnight, you may need to adjust your basal insulin dosage.
Make Gradual Changes: Adjust your basal insulin in small increments to avoid over-correction.
Monitor the Impact: Track your glucose levels after each adjustment to assess the impact.

Bolus Insulin Adjustments:

Assess Post-Meal Glucose Levels: If your glucose levels spike after meals, you may need to increase your bolus insulin dosage.
Consider Carb Ratios: Adjust your insulin-to-carbohydrate ratio based on your CGM data.
Use Pattern Management: Identify patterns in your post-meal glucose levels and adjust your bolus dosages accordingly.

3. Modifying Diet and Lifestyle

CGM data can provide valuable insights into how diet and lifestyle affect glucose levels. Use this information to make informed choices about your meals, exercise routine, and stress management.

Dietary Adjustments:

Monitor Post-Meal Glucose Levels: Track how different foods and meals affect your glucose levels.
Choose Low-Glycemic Foods: Opt for foods with a low glycemic index to minimize glucose spikes.
Balance Carbohydrates, Protein, and Fat: Ensure your meals are balanced to promote stable glucose levels.

Lifestyle Adjustments:

Time Your Exercise: Monitor how exercise affects your glucose levels and adjust your timing accordingly.
Manage Stress: Practice stress-reduction techniques, such as meditation or yoga, to minimize the impact of stress on glucose levels.
Get Enough Sleep: Aim for consistent sleep patterns to support stable glucose levels.

4. Avoiding Hypoglycemia and Hyperglycemia

One of the primary goals of blood sugar management is to avoid hypoglycemia (low blood sugar) and hyperglycemia (high blood sugar). CGMs can help you achieve this by providing alerts and real-time data.

Preventing Hypoglycemia:

Set Low Glucose Alerts: Configure your CGM to alert you when your glucose levels are approaching a low.
Carry Fast-Acting Glucose: Keep a source of fast-acting glucose (e.g., glucose tablets or juice) with you at all times.
Treat Lows Promptly: If your glucose levels drop too low, treat them immediately with fast-acting glucose.

Preventing Hyperglycemia:

Set High Glucose Alerts: Configure your CGM to alert you when your glucose levels are exceeding your target range.
Adjust Insulin Dosages: If your glucose levels are consistently high, work with your healthcare provider to adjust your insulin dosages.
Monitor Meal Portions: Pay attention to your meal portions to avoid overeating.

Troubleshooting Common CGM Issues

Like any technology, CGMs can sometimes experience issues. Here are some common problems and how to troubleshoot them:

1. Sensor Insertion Problems

Problem: Sensor fails to insert properly.

Solution:

Check Expiration Date: Ensure the sensor is not expired.
Inspect Applicator: Make sure the applicator is not damaged.
Rotate Site: Try inserting the sensor at a different site.
Apply Firm Pressure: Use firm, even pressure when inserting the sensor.

2. Inaccurate Readings

Problem: CGM readings do not match blood glucose meter readings.

Solution:

Calibrate the CGM: Follow the manufacturer's instructions to calibrate the CGM.
Check Sensor Placement: Ensure the sensor is properly inserted and secured.
Avoid Pressure on Sensor: Pressure on the sensor can affect accuracy.
Wait for Warm-Up Period: CGMs typically have a warm-up period after insertion before accurate readings are available.
Hydrate: Dehydration can affect interstitial fluid glucose levels.
Take Acetaminophen Cautiously: Use alternative pain relievers if possible or consult with your healthcare provider regarding acetaminophen's potential effect on readings.

3. Sensor Detachment

Problem: Sensor becomes loose or falls off.

Solution:

Clean the Insertion Site: Ensure the insertion site is clean and dry before applying the sensor.
Use Adhesive Overpatches: Apply adhesive overpatches to secure the sensor in place.
Avoid Oily Skin Products: Do not use oily lotions or creams near the sensor insertion site.
Shave Area: If needed, shave the area around the insertion site.

4. Communication Issues

Problem: CGM is not communicating with the receiver or smartphone.

Solution:

Check Bluetooth Connection: Ensure Bluetooth is enabled on your smartphone or receiver.
Restart Devices: Try restarting both the CGM transmitter and your smartphone or receiver.
Replace Transmitter Battery: If the transmitter has a replaceable battery, try replacing it.
Contact Customer Support: If the issue persists, contact the CGM manufacturer's customer support.

5. Skin Irritation

Problem: Skin becomes red, itchy, or irritated at the insertion site.

Solution:

Rotate Insertion Sites: Avoid inserting the sensor in the same spot each time.
Use Hypoallergenic Adhesive: Switch to a hypoallergenic adhesive patch.
Apply a Barrier Film: Use a barrier film or skin protectant before inserting the sensor.
Avoid Tight Clothing: Wear loose-fitting clothing to prevent friction at the insertion site.

Real World Data on CGM Effectiveness

Recent research has consistently shown that using CGMs significantly improves glycemic control and reduces the risk of diabetes-related complications.

A study published in the Journal of the American Medical Association (JAMA) found that individuals with type 1 diabetes who used CGMs had lower A1c levels and spent more time in their target glucose range compared to those using traditional blood glucose monitoring.

The Diabetes Care journal highlighted a study indicating that CGM use in individuals with type 2 diabetes, particularly those on insulin, led to improved glycemic outcomes and reduced hypoglycemia.

| Study | Population | Key Findings | | ---------------------------------------------------------- | ------------------------------- | ---------------------------------------------------------------------------------------------------------------- | | Journal of the American Medical Association (JAMA) | Individuals with type 1 diabetes | Lower A1c levels and more time in target glucose range with CGM use | | Diabetes Care | Individuals with type 2 diabetes | Improved glycemic outcomes and reduced hypoglycemia with CGM use, especially in those on insulin |

Tips for Optimizing CGM Use

To get the most out of your CGM, consider these additional tips:

Stay Hydrated: Adequate hydration supports stable glucose levels and accurate CGM readings.
Keep a Food Diary: Record what you eat and how it affects your glucose levels to identify patterns and make informed dietary choices.
Track Exercise: Monitor how different types of exercise impact your glucose levels and adjust your routine accordingly.
Communicate with Your Healthcare Provider: Regularly share your CGM data with your healthcare provider to optimize your diabetes management plan.
Attend Diabetes Education Programs: Participate in diabetes education programs to learn more about CGM technology and blood sugar management.
Join Support Groups: Connect with other CGM users to share experiences and tips.
Take advantage of Manufacturer Resources: CGM manufacturers often provide educational resources, support materials, and online tools.

The Future of CGM Technology

The future of CGM technology looks promising, with advancements in sensor accuracy, data integration, and user convenience.

Improved Sensor Accuracy: Ongoing research is focused on developing more accurate and reliable sensors.
Artificial Intelligence (AI): AI algorithms are being used to analyze CGM data and provide personalized insights and recommendations.
Integration with Insulin Pumps: Closed-loop systems (artificial pancreas) that automatically adjust insulin delivery based on CGM readings are becoming more common.
Smaller, More Discreet Sensors: Efforts are underway to develop smaller and more discreet sensors that are easier to wear.
Non-Invasive CGMs: Researchers are exploring non-invasive CGM technologies that do not require sensor insertion.

Conclusion

Using a continuous glucose monitor (CGM) can significantly improve blood sugar management and quality of life for people with diabetes. By providing real-time data, trend information, and customizable alerts, CGMs empower users to make more informed decisions about their health. Follow this guide to use your CGM effectively, interpret the data, and troubleshoot common issues. Consult with your healthcare provider to personalize your CGM settings and optimize your diabetes management plan. With consistent use and proactive management, CGMs can help you achieve better glycemic control and reduce the risk of diabetes-related complications. Safe Ways To Lower Blood Sugar Quickly During A Spike